1. Two methods for measurement of rectal potential difference in man were compared. A saline-filled catheter technique gave more reproducible results and was better tolerated by patients than the solid probe technique.
2. Infusion of amiloride at a concentration of 4 × 10−6 mol/l in saline produced a variable fall of potential difference in six normal subjects. Dose-response curves in two subjects showed that complete inhibition of rectal potential difference occurred at 4 × 10−5 mol/l and 4 × 10−6 mol/l respectively.
3. This finding provides additional evidence that rectal potential difference in man results from electrogenic ion transport across the mucosal epithelial cell.